nettest: use RoutedInterface for probing network stack capability

The ipv4/ipv6 support capability is done by explicitly listening on
loopback interface. However, it can lead to false positive, especially
for ipv6 case. For example, ipv6 can be enabled, but explicitly disable
for loopback interface (for security, policy ...).

This CL changes probeStack to use another approach, by looking for any
interface that can route IP traffic and in "UP" state. If there's one,
then the platform can do ipv4/ipv6 networking functionality.

Fixes golang/go#57386

Change-Id: If911bc223b52c5a4562d3f61b4ee1032bdbec47c
Reviewed-on: https://go-review.googlesource.com/c/net/+/458096
TryBot-Result: Gopher Robot <[email protected]>
Auto-Submit: Cuong Manh Le <[email protected]>
Reviewed-by: Benny Siegert <[email protected]>
Reviewed-by: Matt Layher <[email protected]>
Run-TryBot: Cuong Manh Le <[email protected]>
Reviewed-by: David Chase <[email protected]>

Author: cuonglm

ipv6/bpf_test.go

@@ -19,8 +19,8 @@ func TestBPF(t *testing.T) {
 	if runtime.GOOS != "linux" {
 		t.Skipf("not supported on %s", runtime.GOOS)
 	}
-	if !nettest.SupportsIPv6() {
-		t.Skip("ipv6 is not supported")
+	if _, err := nettest.RoutedInterface("ip6", net.FlagUp|net.FlagLoopback); err != nil {
+		t.Skip("ipv6 is not enabled for loopback interface")
 	}
 
 	l, err := net.ListenPacket("udp6", "[::1]:0")

ipv6/readwrite_test.go

@@ -223,10 +223,10 @@ func TestPacketConnConcurrentReadWriteUnicastUDP(t *testing.T) {
 	case "fuchsia", "hurd", "js", "nacl", "plan9", "windows":
 		t.Skipf("not supported on %s", runtime.GOOS)
 	}
-	if !nettest.SupportsIPv6() {
-		t.Skip("ipv6 is not supported")
+	ifi, err := nettest.RoutedInterface("ip6", net.FlagUp|net.FlagLoopback)
+	if err != nil {
+		t.Skip("ipv6 is not enabled for loopback interface")
 	}
-
 	c, err := nettest.NewLocalPacketListener("udp6")
 	if err != nil {
 		t.Fatal(err)
@@ -236,7 +236,6 @@ func TestPacketConnConcurrentReadWriteUnicastUDP(t *testing.T) {
 	defer p.Close()
 
 	dst := c.LocalAddr()
-	ifi, _ := nettest.RoutedInterface("ip6", net.FlagUp|net.FlagLoopback)
 	cf := ipv6.FlagTrafficClass | ipv6.FlagHopLimit | ipv6.FlagSrc | ipv6.FlagDst | ipv6.FlagInterface | ipv6.FlagPathMTU
 	wb := []byte("HELLO-R-U-THERE")
 

ipv6/sockopt_test.go

@@ -20,8 +20,9 @@ func TestConnInitiatorPathMTU(t *testing.T) {
 	case "fuchsia", "hurd", "js", "nacl", "plan9", "windows", "zos":
 		t.Skipf("not supported on %s", runtime.GOOS)
 	}
-	if !nettest.SupportsIPv6() {
-		t.Skip("ipv6 is not supported")
+
+	if _, err := nettest.RoutedInterface("ip6", net.FlagUp|net.FlagLoopback); err != nil {
+		t.Skip("ipv6 is not enabled for loopback interface")
 	}
 
 	ln, err := net.Listen("tcp6", "[::1]:0")
@@ -53,8 +54,8 @@ func TestConnResponderPathMTU(t *testing.T) {
 	case "fuchsia", "hurd", "js", "nacl", "plan9", "windows", "zos":
 		t.Skipf("not supported on %s", runtime.GOOS)
 	}
-	if !nettest.SupportsIPv6() {
-		t.Skip("ipv6 is not supported")
+	if _, err := nettest.RoutedInterface("ip6", net.FlagUp|net.FlagLoopback); err != nil {
+		t.Skip("ipv6 is not enabled for loopback interface")
 	}
 
 	ln, err := net.Listen("tcp6", "[::1]:0")

ipv6/unicast_test.go

@@ -23,8 +23,8 @@ func TestPacketConnReadWriteUnicastUDP(t *testing.T) {
 	case "fuchsia", "hurd", "js", "nacl", "plan9", "windows":
 		t.Skipf("not supported on %s", runtime.GOOS)
 	}
-	if !nettest.SupportsIPv6() {
-		t.Skip("ipv6 is not supported")
+	if _, err := nettest.RoutedInterface("ip6", net.FlagUp|net.FlagLoopback); err != nil {
+		t.Skip("ipv6 is not enabled for loopback interface")
 	}
 
 	c, err := nettest.NewLocalPacketListener("udp6")

ipv6/unicastsockopt_test.go

@@ -19,8 +19,8 @@ func TestConnUnicastSocketOptions(t *testing.T) {
 	case "fuchsia", "hurd", "js", "nacl", "plan9", "windows":
 		t.Skipf("not supported on %s", runtime.GOOS)
 	}
-	if !nettest.SupportsIPv6() {
-		t.Skip("ipv6 is not supported")
+	if _, err := nettest.RoutedInterface("ip6", net.FlagUp|net.FlagLoopback); err != nil {
+		t.Skip("ipv6 is not enabled for loopback interface")
 	}
 
 	ln, err := net.Listen("tcp6", "[::1]:0")
@@ -64,8 +64,8 @@ func TestPacketConnUnicastSocketOptions(t *testing.T) {
 	case "fuchsia", "hurd", "js", "nacl", "plan9", "windows":
 		t.Skipf("not supported on %s", runtime.GOOS)
 	}
-	if !nettest.SupportsIPv6() {
-		t.Skip("ipv6 is not supported")
+	if _, err := nettest.RoutedInterface("ip6", net.FlagUp|net.FlagLoopback); err != nil {
+		t.Skip("ipv6 is not enabled for loopback interface")
 	}
 
 	ok := nettest.SupportsRawSocket()

nettest/nettest.go

@@ -34,12 +34,10 @@ var (
 )
 
 func probeStack() {
-	if ln, err := net.Listen("tcp4", "127.0.0.1:0"); err == nil {
-		ln.Close()
+	if _, err := RoutedInterface("ip4", net.FlagUp); err == nil {
 		ipv4Enabled = true
 	}
-	if ln, err := net.Listen("tcp6", "[::1]:0"); err == nil {
-		ln.Close()
+	if _, err := RoutedInterface("ip6", net.FlagUp); err == nil {
 		ipv6Enabled = true
 	}
 	rawSocketSess = supportsRawSocket()